I. Field of the Invention
The present invention relates to a member for the guidance of a movable piece, for example of a shaft or a cylindrical rod movable in rotation and/or in translation, or else of a swiveling piece.
II. Discussion of the Background
It is a known practice to use cylindrical rings to provide a precise positioning of a shaft while providing its guidance in rotation or in sliding. To make the movement easier while reducing the wear of the friction surfaces, materials with a low friction coefficient and a good wear-resistance are used. These materials may form the totality of the rings or be used in thin layers placed on the supports providing a mechanical resistance of the thin layers.
For example it is a known practice to use rings made of metal or metal alloy, such as a bronze alloy, with, in some cases, a surface glaze to improve the sliding of the shaft.
Other rings, usually used dry without additional lubricant, are produced in a single piece of plastic or comprise a metal support or sleeve ensuring the mechanical resistance, with a coating of the guide surfaces with a material with a low friction coefficient.
In certain applications, these rings are subject to severe stresses, for example heavy pressure, high sliding speed or high temperature, often with vibrations and impacts transmitted by the shaft to be guided, which results in rapid wear and a risk of destruction of these rings.
If metal rings are used to reduce the wear and increase the service life, seizing problems are noted eventually.
It has also been proposed to use ceramic rings, this material having a high degree of hardness and a relatively low friction coefficient, for example approximately 0.3, and a very good resistance to many physical or chemical agents.
In addition, these rings are produced by sintering, which allows complex shapes to be produced easily. However they have the disadvantage of having a very high rigidity, a zero elasticity and a fragility to impacts, which poses problems of resilience because these rings do not deform and, in the event of wear, the contact surfaces deteriorate and a functional clearance appears which may lead to the breakage of the rings.
These problems of wear and failure of the anti-friction rings may have consequences particularly in the aerospace industry where the wear and breakage of a bearing may lead to the stoppage or destruction of an engine.